1. Field of the Invention
This invention relates to the prevention of blow-outs in oil wells during the early stages of drilling when conventional blow-out preventers which seal the well are of limited effectiveness owing to the tendency of the unwanted fluid to force itself up outside the casing. More specifically this invention provides a diverter valve of simplified construction which reduces maintenance problems during use in the field.
2. Description of the Prior Art
A type of diverter valve currently in use for the purpose of preventing blow-outs during the early stages of drilling is described in U.S. Pat. No. 3,917,008. The problems which such a diverter valve is designed to solve are set forth in that patent, and the invention described and claimed in that patent is a diverter valve which is opened and closed by the movement of a piston within a cylindrical sleeve. The piston has a mud-contact end against which is exerted the back-pressure at the surface of the annulus between the drill string and the casing. The other end of the piston is a biased end against which controllable gas pressure is exerted. The cylindrical sleeve has a mud diverter conduit extending from a diverted-mud outlet opening in the side of the cylindrical sleeve. In the closed position, the piston covers the outlet opening. When abnormally high pressure is encountered at the bottom of the well, the resultant high pressure at the surface of the annulus between the drill string and the casing overcomes the opposing pressure being exerted against the biased end of the piston so as to move it within the cylindrical sleeve in such a manner as to uncover the diverted-mud outlet opening, permitting the mud to escape through the mud diverter conduit.
While the diverter valve of said U.S. patent is of elegant construction, it is unsuited to the rugged conditions in the field which are characteristic of oil well drilling rigs. The various parts of such diverter valves tend to be corroded by the moist gases encountered during operation of the rig, and improper operation often results during use for these and other reasons. The repairs needed to correct such improper operation are difficult to carry out, and the replacement parts required are difficult to obtain. There is nothing delicate in an oil field operation, and components used on drilling rigs are preferably of rugged construction, easy to repair. The diverter valve of the prior art, as shown in said U.S. patent and as currently used in the field, is very complicated, using nitrogen pressure and elaborate components. However, it is not rugged; it is easily damaged; and it is difficult to fix it in the field. It has close tolerances, and cement gets into the device and jams it. It is also jammed when wet air gets into it instead of nitrogen.